Drying of yarn by dielectric heating



Dec. 23, 1958 w. c. RUDD 2,866,063

DRYING OF YARN BY DIELECTRIC HEATING Filed Dec. 28, 1955 Q INVENTOR. MLLAcECEz/oo.

v yarn is obtained.

United States Patent DRYING OF YARN BY DIELECTRIC HEATING Wallace C. Rudd, Larchmont, N. Y., assignor to Magnetic Heating Corp., New Rochelle, N. Y., a corporation of New York Application December 28, 1955, Serial No. 555,979

3 Claims. (Cl. 219-1053) This invention relates to apparatus and methods for drying textile fibers or yarn and the like by dielectric heating and is particularly adapted among other possible uses for the drying of so-called cakes of rayon or other synthetic yarn to remove a greater part of the moisture content therefrom after the yarn has been spun into such cakes.

Yarn such as of rayon as formed during the manufacture thereof into so-called cakes usually has a heavy moisture content which by weight may equal as much as the weight of the yarn. In order to remove such moisture content down to the usually desired range of about 5% to 8%, it has long been the practice to dry the yarn cakes in an oven which may require as long as several days. More recently, however, it has been found possible to dry such cakes by dielectrically heating the same for a relatively short period, for example from 5 to 15 minutes and with the further result that an improved quality of In drying such cakes in an oven, the outside portions dry first and thus tend to shrink against the wet inside portions. Since such shrinkage cannot occur to a substantial degree before the inside portions become dried and shrink to a reduced diameter, the result is that the turns of yarn around the outside of the cake are caused to stretch, with the outer fibers stretched differently than the inner ones. Consequently the various portions of the fibers have different susceptibilities to dyeing and thus objectionable variations of color may appear in the finished cloth. These difficulties, however, may in many cases be largely although not wholly avoided by drying the cakes by dielectric heating, as disclosed for example in the United States patent to J. E. Phillips Ir. No. 2,635,352, granted April 21, 1953 and reference to which is hereby made for an explanation of the general method and means as to which the present invention constitutes an improvement. The dielectric heating method of drying such rayon cakes in general has the advantage that the inner portions of the cakes are dried first or at least not later than the outer portions, thus allowing uniformity of shrinkage and a general approximation of uniformity of drying.

I According to the method disclosed in the above mentioned Phillips patent, electrodes connected to a high frequency source of current are placed at each side of the rayon cakes close to the periphery thereof and the cakes are continuously rotated at constant speed about their vertical axes, such rotation representing an effort to provide uniformity of action of the dielectric field between the electrodes on the various parts of the cakes located therebetween.

However, since such cakes are formed with a central hole therein, such hole constitutes in effect an air core having a dielectric constant of 1, with the result that the greater part of the electrical field avoids such hole and is constrained to travel from one electrode to the other in directions more or less circumferentially Within portions of the cake, inasmuch as the dielectric constant of the material of the cake is much higher, for example in the neighborhood of 4 or 5 instead of the constant of l for the hole within the cake. For these reasons the inner and outer turns of yarn are not concurrently and uniformly heated to the degree which would be desirable for producing a uniform product, that is to say, a product in which all turns of the yarn would be relatively free of stretching to the same degree as well as yarn in which all portions of the cross-section thereof would be uniform.

In accordance with the present invention, the above noted shortcomings of dielectrically heating such cakes of yarn may be overcome by rotating the cakes preferably with the central hole therein in vertical position, between a pair of electrodes at opposite sides of the cakes and connected respectively to the two terminals of high fre quency current source, and with an intermediate electrode in the form, for example, of a metal cylinder located within the hole in the cake and insulated from the circuit of the two other electrodes. Such cylinder may be either suspended in stationary position or may rotate with the cake and its support. Furthermore, the cake need not necessarily be rotated constantly or at constant speed, but may be turned intermittently or at gradually increasing or decreasing speeds, as circumstances may warrant. But with such an insulated intermediate electrode located in the hole within the cake, the air core is in effect largely eliminated and in such manner that the electrical field or the greater portion thereof will follow paths directly from one of the side electrodes through one side of the cake generally at right angles to the electrode plate, and to the metal cylinder, then through the other side of the cake also generally at right angles to the electrode plates. It has been found that by this method and means, variations in the shrinkages in the fibers in the different parts of the cake as well as within the cross-sections of the individual fibers are very substantially more completely avoided than with any prior known practices.

Various further and more specific objects, features and advantages of the invention will appear from the descrip tion given below taken in connection with the accompanying drawings illustrating by way of example a preferred form of the invention.

In the drawings:

Fig. 1 is a vertical sectional view illustrating somewhat schematically one embodiment of the invention;

Figure 2 is a top plan view of same;

Fig. 3 is a schematic diagram showing approximately the electrical field distribution which is believed to occur in a rayon cake which is being dried according to the method of the above-mentioned Phillips patent; and

Fig. 4 is a corresponding view but showing the approximate conditions which occur with the method of the present invention.

As shown in Fig. 1, a rayon yarn cake is indicated in vertical cross-section at 10, resting upon a rotatable platform or support comprising a suitable insulation disc 12 carried on insulation supporting posts 13 which in turn are carried upon a rotatable disc 14. The disc 14 may be supported as by spindle 15 adapted to be rotated or turned either at constant speed, intermittently or at progressively changing speeds through any suitable gearing such as schematically indicated at 16. A pair of electrodesas at 17 and 18 is mounted on suitable supports (not shown) at opposite sides of the cake 10, these electrodes being connected, as shown, to a source of high frequency current, for example a current of the order of magnitude of one hundred thousand cycles per second or preferably higher, within the range of about 1 to 50 megacycles and of a voltage which may for example vary from 3000 to 25,000 volts.

Within the interior of the cake 10, that is, within the central hole 21 thereof, an intermediate electrode in the ably non-ferrous metal.

form of a metal cylinder 20 is provided. In the form here shown, this cylinder is supported and rotated by the disc 12 but it will be understood that it might be otherwise and non-rotatably' supported, if desired. This cylinder should be of a length at least about equal to the vertical dimension of the hole 21 in the cake and of a diameter sufiicient to fill the greater part of such hole, but with clearance sufficient to facilitate relative removal of the cake and cylinder and to permit air to flow up around same. This cylinder need only have quite thin walls, for example several millimeters in thickness, although for permanence and strength, it may be made with a wall thickness of and formed preferably of copper or other good conductive and prefer- While as shown in Fig. 1, this intermediate electrode preferably has an external diameter extending over the greater part of the diameter of the hole in the cake, yet the diameter of the electrode 20 is preferably selected as such that its external surfaces will, as shown, be spaced substantially from the internal surfaces in such hole. Otherwise the internal surface portions of the yarn cake may become overheated as compared with the outer portions of the cake. Fig. 1 shows appropriate proportions for the relative sizes of the intermediate electrode and the hole in the cake for a typical case, and it will be apparent that an electrode 20 of appropriate size may be selected by trial so that the inner portions of the cake will not become overor under-heated as compared with the outer portions.

The rotating insulation disc 12 is preferably formed with a circular series of vent holes as at 22 to allow air to rise up therethrough and through the space surrounding the cylinder 20 and between such cylinder and the inner surfaces of the cake to facilitate more rapid drying of the latter.

With the arrangement as shown in Figs. 1 and 2, the various portions of the electrical field between the electrodes 17 and 18 will assume positions such as generally indicated by the dotted lines in Fig. 4, that is, the field Will follow paths transversely through the sides of the cake nearest the electrodes and thus generally perpendicularly to the electrode plates and approximately parallel to a diameter of the cake, this being because the field of each electrode 17, 18 will extend therefrom along fairly direct paths to the intermediate cylindrical electrode 24 On the other hand, in the absence of the intermediate cylindrical electrode 20, the various portions of the field between the side electrodes will tend to follow paths such as indicated at 25 and 26 in Fig. 3. That is, the field in efiect will tend to shun the central air core 21 in the cake and to follow paths having the much higher dielectric constant, more or less circumferentially through the regions indicated at 25 and 26, but Without uniformly permeating these regions and without subjecting the inner regions of the cake to such extended heating eifects as the intermediate or outer regions. Thus with the heretofore known field distribution as generally indicated in Fig. 3, there will he usually some considerable non-uniformity in the stretching of the yarn and the consequent degree of uniformity of the dried yarn, whereas the field of distribution as indicated in Fig. 4, this difficulty will be substantially eliminated.

It will be understood that variations of the cake supporting arrangements and of the construction and arrangement of the side electrodes may be made according to the various examples disclosed in the above-mentioned Phillips patent, but in each case according to the Cil present invention the intermediate cylindrical electrode such as at 20 is added and suitably supported. It will be further understood that the electrode 20 need not necessarily be cylindrical in shape or hollow, although such construction is preferred for best results.

What is claimed and desired to be secured by Letters Patent is:

1. Apparatus for drying fiber, yarn and the like which has been wound into cakes having a central hole, comprising: a support upon which the cake is adapted to rest with the central hole in vertical position; means for turning said support about the axis of the hole; a pair of substantially parallel electrode plates mounted respec-. tively at opposite sides of the position on the support at which the cake is adapted to be located; a source of high frequency electrical heating current having its two terminals respectively connected to said electrodes; and an intermediate electrode insulated from the other two and the circuit thereof and positioned and shaped to occupy the greater part of the space within the central hole in the cake when resting upon such support, the external surfaces of said intermediate electrode however being spaced substantially from the internal surfaces in the hole in the cake.

2. Apparatus for drying fiber, yarn and the like which has been wound into cakes having a central hole, comprising: a support upon which the cake is adapted to rest with the central hole in vertical position; means for turning said support about the axis of the hole; a pair of substantially parallel electrodes mounted respectively at opposite sides of the position on the support at which the cake is adapted to be located; a source of high frequency electrical heating current having its two terminals respectively connected to said electrodes; and an intermediate electrode in the form of a metal cylinder insulated from the other two electrodes and the circuit thereof and positioned within the central hole in the cake when resting upon such support.

3. Apparatus for drying fiber, yarn and the like which has been wound into cakes having a central hole, comprising: a support upon which the cake is adapted to rest with the central hole in vertical position; means for turning said support about the axis of the hole; a pair of substantially parallel electrodes mounted respectively at diametrically opposite sides of the position on the support at which the cake is adapted to be located, said electrodes being generally at right angles to a diameter of the position of said central hole; a source of high frequency electrical heating current having its two terminals respectively connected to said electrodes; and an intermediate electrode insulated from the other two and the circuit thereof and positioned within the central hole in the cake when resting upon such support and adapted to cause the electrical field between the side electrodes to follow paths transversely across the fiber or yarn within the side portions of the cake, said intermediate electrode being substantially coaxial with the hole in the cake, and having an external diameter extending over the greater part of the diameter of the hole in the cake but the external surface of such intermediate elec trode being spaced substantially from the internal surfaces in such hole.

References Cited in. the file of this patent UNITED STATES PATENTS 2,263,681 Hart Nov. 25, 1941 2,479,351 Hagopian Aug. 16, 1949 2,582,806 Van Nes et al. Jan. 15, 1952 

